Recovering oil from oil containing reservoirs can include three distinct phases. During a first phase, natural pressure of the oil containing reservoir and/or gravity can drive oil into a wellbore, and combined with an artificial lift technique, such as pumping, bring the oil to the surface. However for some oil recovery processes, in the first phase only about 10 percent of the oil containing reservoirs' original oil in place is recovered.
A second phase, to extend the productive life the oil containing reservoir, can increase oil recovery to 20 to 40 percent of the original oil in place. For some applications, the second phase can include injecting water to displace oil and drive it to a production wellbore. In some applications, re-injection of natural gas has been employed to maintain and/or increase pressure in the oil containing reservoir, as natural gas is often produced simultaneously with the oil recovery.
However, with much of the easy-to-recover oil already recovered via the first phase and/or the second phase, a third phase of oil recovery has been developed. The third phase may be referred to as enhanced oil recovery. Enhanced oil recovery techniques offer prospects for producing more of the oil containing reservoirs' original oil in place, thus further extending the productive life of the oil containing reservoir. One estimate of oil in place that is not recoverable by the first phase of oil recovery or the second phase of oil recovery that could be the targeted by enhanced oil recovery techniques is 377 billion barrels of oil in place. Enhanced oil recovery can include an injection of fluids other than water, such as steam, gas, surfactant solutions, or carbon dioxide.
For some applications the injected fluid is miscible with the hydrocarbons in the oil containing reservoir. This injected fluid can help reduce the viscosity of oil present in the oil containing reservoir in order to increase the flow of oil to the production wellbore.
Enhanced oil recovery, however, can be accompanied with a number of drawbacks. One problem encountered is poor sweep of the oil containing reservoir. Poor sweep can occur when carbon dioxide injected into the oil containing reservoir flows through the paths of least resistance due to the low viscosity of the carbon dioxide, thus bypassing significant portions of the oil containing reservoir and the oil located there. When the carbon dioxide bypasses significant portions of the oil containing reservoir, less oil is contacted with the carbon dioxide, reducing the likelihood that the carbon dioxide will reduce the viscosity of the oil, thus producing poor sweep. In addition, due to the low density of the carbon dioxide, the injected carbon dioxide can rise to the top of the oil containing reservoir and “override” portions of the oil containing reservoir, leading to early breakthrough of the carbon dioxide at the production wellbore, leaving less carbon dioxide within the oil containing reservoir to contact with the oil, again reducing the likelihood that the carbon dioxide will reduce the viscosity of oil.
To increase the enhanced oil recovery process effectiveness, a surfactant can be been used to generate an emulsion in the oil containing reservoir. An emulsion can generate an apparent viscosity of about 100 to about 1,000 times that of the injected carbon dioxide, therefore, the emulsion can inhibit the flow of the carbon dioxide into that portion of the oil containing reservoir that has previously been swept. In other words, the emulsion can serve to block the volumes of the oil containing reservoir through which the carbon dioxide can short-cut, thereby reducing its tendency to channel through highly permeable fissures, cracks, or strata, and directing it toward previously unswept portions of the oil containing reservoir. As such, the emulsion can help force the carbon dioxide to the recoverable hydrocarbons in the less depleted portions of the oil containing reservoir.